For example in electronic apparatuses such as personal computers, a conventional air-cooling type cooling system is no longer effective because of the progress in operating speed and expansion of functions, as well as because of the demand for reduction in dimensions of the apparatus, and a water-cooling type cooling system has now taken its place. The water-cooling type cooling system typically includes a diaphragm pump incorporated with a piezoelectric vibrator or the like that vibrates a wall of a pump chamber, to thereby intake and discharge a liquid fluid. FIG. 11 is a cross-sectional view of a popular diaphragm pump conventionally employed. As shown in FIG. 11, a casing 40 includes orifices communicating with a pump chamber 45, and an inflow check valve 41 and an outflow check valve 42 are installed so as to cover the respective orifice. At the respective end portions of the casing 40, an inlet port 43 and an outlet port 44 are provided. Above the casing 40, a piezoelectric vibrator 47 is located by means of a pump chamber tight seal 46, and an end portion of the piezoelectric vibrator 47 is press-fixed by a pump cover 48.
In the diaphragm pump thus constructed, when the piezoelectric vibrator 47 is activated by a current so as to vibrate up and downward alternately, the inflow check valve 41 and the outflow check valve 42 are caused to alternately open (alternately close), so that a cooling fluid introduced through the inlet port 43 flows through the pump chamber 45 and is discharged through the outlet port 44. While the fluid is being conveyed, a bubble contained in the fluid also moves into and out of the pump chamber. It is preferable to promptly drive out the bubble from the pump chamber, because the presence of the bubble affects the fluid conveying characteristic. Accordingly, various proposals have been made so far on the measures for smoothly discharging the bubble from the pump chamber.
For example, the patent document 1 teaches increasing the pressure in the pump chamber with a heater provided around the pump chamber, to thereby discharge the bubble. The patent document 2 proposes forming a groove between an intake valve and an exhaust valve of the pump chamber so as to increase the flow speed of the fluid and to thereby discharge the bubble, and locating the exhaust valve at a position higher than the intake valve, so as to let the bubble escape. Also, the patent document 3 proposes a structure that causes the fluid to be introduced into the pump chamber in a large curvature toward a peripheral portion thereof, thereby facilitating discharging the bubble.
The diaphragm pump is a volume-variable pump, and higher discharge pressure is one of the features thereof. Generally, a pump that provides higher discharge pressure can quickly discharge the bubble that has intruded into the pump chamber, through the outlet port. Even with the diaphragm pump which offers high discharge pressure, however, in case that the bubble intrudes into the pump chamber when the pump is connected to a passage that imposes high flow resistance (pressure loss), the bubble incurs the disadvantage of offsetting the discharge pressure of the pump and thereby decreasing the flow rate. The conventional diaphragm pump, typically exemplified by the piezoelectric pump, normally includes the inlet port at an end portion of the pump chamber and the outlet port at the other end portion, or both ports at the respective end portions. Besides the inlet port and the outlet port are of the same caliber. Therefore, the bubble that has once intruded into the pump chamber is detained along the peripheral portion of the pump chamber by the influence of the flow status within the chamber, and the influence of the viscosity and the surface tension of the fluid, and is difficult to be driven out. The diaphragm pumps according to the patent documents 1 to 3 have respectively undergone some improvements, but not yet to perfection.
An object of the present invention is to solve the problem incidental to the foregoing conventional art, and to provide a highly reliable diaphragm pump capable of quickly discharging a bubble that has intruded into the pump chamber, and thereby assuring the performance under a stable flow rate.
[Patent document 1] JP-A No. 2005-133704
[Patent document 2] JP-A No. 2003-035264
[Patent document 3] WO2001/066947